At the present time the general treatment of organ transplant rejection is accomplished with the use of medications such as azothioprine, prednisone and cyclosporine. The lack of specificity of these drugs produces side effects that limits their dose and thus their effectiveness in immunosuppression. Treatment with the newest drug cyclosporine is expensive, costing several dollars per day and must be taken for the lifetime of the patient. Some patients cannot afford this financial burden and in addition cyclosporine can damage kidneys. Survival of kidney grafts from unrelated donors after one year is approximately 50% and acute rejections that are resistant to drug treatment invariably fall, P. J. Morris (1985) Transplant Proceedings Vol XVII No 1 p 1153. Immunological rejection is still the main cause of loss of transplanted organs, and better treatments are needed.
The current invention is a monoclonal antibody (MA) that has been shown to very effectively reverse kidney graft and corneal graft rejections without adverse side effects. It represents a new approach to the treatment of transplantation rejection in general. It offers new hope to many patients who need transplants of hearts, lungs, liver, bone marrow and other organs without fear of dying from rejection. MAs have been claimed to hold much promise as new antirejection agents (P J Morris, supra),
MAs are secreted from hybrid cells called hybridomas. The hybrid cells are made by fusing spleen cells from immunised normal mice and cancer cells called myelomas from the same species. The mice are immunised with cells that express the antigan that one desires a monoclonal antibody (MA) against. Following the fusion hybridomas are selected for those that secrete antibodies against desirable antigens. The hybridoma inherits the normal cell's ability to manufacture antibodies and the cancer cell's capacity to divide. This produces a cell line grown in culture that continuously secretes an unlimited supply of homogeneous antibodies. Therefore mass production of the antibody is a feature suitable for therapeutic uses. The antigenic determinant against which the MA reacts determines the potential value of the hybridoma and the MA. The subject MA (CBL1) reacts with a unique antigen which is found almost entirely on actively dividing cells such as stimulated lymphocytes (called blast cells) and cancer cells of all types. The antigan is located on the cell membrane and controls the growth and division of these cells.
The subject MA antibody (CBL1) has potential in the treatment of transplant rejection because of its specific toxicity against the cells that are actually causing the rejection of the grafts, i.e. a small percentage of activated lymphocytes. Other monoclonal antibodies such as OKT3 have been used for reversing transplant rejection but the results are disappointing. Cosimi et al (1981) New Engl J. Med 305. The OKT3 MA reacts with all T lymphocytes in the body not just those few that are actively involved in the rejection of the graft. This results in side effects and lack of prolonged effectiveness very similar to side effects seen by drug therapy. Most of the lymphocytes in the body are not dividing and not involved in graft rejection. More effective antirejection and anticancer agents will be specific for dividing cells.
Chemotherapy for cancer has improved survival in some cancers such as childhood leukemia but the survival rate for advanced (metastatic) solid tumors has not dramatically increased in over 30 years. When cancer cells are detected in tissues distant from the primary site then the outcome is usually fatal.
The National Institute of Health recognises these problems and has advocated a serious investigation into newer treatments. Among the most hopeful are monoclonal antibodies and growth factors that will have fewer side effects.
Clinical trials with tumor associated antibodies have been described but thus far with limited success. (Cancer, Devita et al. 1985 Cancer, Lippincott Company, Philadelphia, p 133 and 2244). Although MA directed against tumor antigens provide optimism for adjuvant cancer therapy the lack of specificity of MA tried thus far has limited their effectiveness. Growth factors have not yet been described in clinical trials.
The antigenic determinant of CBL1 appears to be a specific type of tumor related growth factor. Growth factor is a general term for molecules that stimulate and control the growth of cells mainly by binding initially to the cell membrane. Most cells in the body are in a slow growth or non dividing state. The majority of peripheral blood lymphocytes are not dividing unless they are activated by foreign antigens. Cancer cells are rapidly dividing cells of uncontrolled growth. Growth factor binds to the cell membrane and allows nutrients to enter the cell which promote these changes in growth characteristics. (Cancer, Devita et al. 1985, p 50 supra).
Cells growing in cultured nutrient medium require serum as a source of growth factors, (Gospodarowit Det al. Ann. Rev. Biochem. 451, 531 1976). Several of these serum growth factors have now been identified and purified; some are hormones such as insulin, erythropoietin and others are polypeptides that promote growth of certain normal tissue cells such as fibroblast growth factor, epidermal growth factor, nerve growth factor, platelet derived growth factor, transferrin. Interleukin 2 is a growth factor for activated normal T lymphocytes. Autocrine growth factors are produced by cancer cells themselves possibly from viral DNA integrated into the cell genetic material. They are shed into the cellular environment such as culture medium and cause further growth and cell division. (Cancer, Edited by V. T. Devita et al. 1985 p50 supra).
A monoclonal antibody Tac has been reported (Uchiyama et al. J. Immunol. 1981, 126 1393-1397). It appears to react with the interleukin 2 receptor present on activated T lymphocytes but not present on the majority of leukemia cells. However CBL1 has a different antigenic specificity to the Tac antibody. CBL1 reacts with leukemia cell lines but Tac does not. The molecular weight of the CBL1 antigenic determinant is 15,000 daltons. This in addition to its reactivity pattern distinguishes it from other MAs described against activated lymphocytes. MAs that react with growth factors that control the growth of lymphoid cells and cancer cells have not been described. CBL1 can be distinguished by the molecular weight and tissue distribution of the antigenic determinant from the following MAs which react with activated lymphocytes. None of these antibodies has yet been described as a useful therapeutic agent. Omary et el. (1980) Nature 286 888-891 (B3-25 cell line); Haynes et al. (1981) J. Immunol. 127: 347-351 (5E9 cell line); and Reinherz et al. (1980) PNAS 77: 1581-1592 (OKT9 cell line). A polyclonal rabbit antiserum designated 157 which is specific for blast cells and peripheral blood monocytes has been developed. Billing et al. (1979) Clin. Immunol. Immunopathol. 13: 435-443. All of the MAs, 157, B3-25, 5E9 and OKT9 react with the transferrin receptor of 180,000 daltons consisting of two equal protein chains of 90,000 daltons. 4F2 (Haynes et al. 1981 J. Immunol. 126, 1409-1414) reacts with an antigan of 120,000 daltons which consists of polypepetides of 40KD and 80KD and is resistant to proteolysis. The CBL1 antigan is a 15K dalton molecule which is not resistant to proteolysis.